SBRT yields excellent Ca control, low rate of severe toxicity

Results from a multicenter study show progression-free survival in 97% of low- and intermediate-risk prostate cancer patients.

Men newly diagnosed with low- or intermediate-risk prostate cancer can experience low severe toxicity, shorter treatment times, and excellent cancer control rates through the use of high-dose stereotactic body radiation therapy (SBRT), according to a study presented at the American Society for Radiation Oncology annual meeting in Boston.

SBRT precisely targets high doses of radiation to the tumor in small number fractions, simultaneously avoiding surrounding tissue and reducing toxicity to non-cancerous cells. When treating tumors in the prostate, SBRT avoids the adjacent bladder, sex organs, and rectum.

“We had this new technology that was promising for treating prostate cancer more quickly and more accurately and also could give a higher dose of radiation to the gland. We hoped to prove in a multicenter setting that it was safe and the toxicity would be accessible, but we also hoped to show that because we were giving a biologically higher dose, we could improve on cancer relapse rates,” said first author Robert Meier, MD, of Swedish Medical Center, Seattle.

In an open-label study, Dr. Meier and co-authors studied 309 men with newly diagnosed prostate cancer who were tested at 21 community, regional, and academic hospitals across the U.S. All of the men had either low-risk disease (CS T1-T2a, Gleason 6, PSA <10 ng/mL) (n=172) or intermediate-risk disease (CS T1c-T2b with either Gleason 7 and PSA <10 ng/mL, or Gleason 6 and PSA 10-20 ng/mL).

“The men received SBRT via a non-isocentric robotic platform, with an RT dose to the prostate of 40 Gy administered in five treatment sessions of 8 Gy each,” Dr. Meier said. “Those with intermediate risk received a dose of 36.25 Gy to the seminal vesicles.”

The results revealed that at 5 years’ follow-up, 97% of patients treated with SBRT remained cancer free, and only 2% experienced any serious side effects.

Next: “I expected low risk to do well (97.3%) but didn’t figure intermediate risk to show 97%; that’s better than I thought.”

“To start with, toxicity was really low. We had felt a rate of grade 3-5 at 5 years of 10% would be unacceptable and it turned out to be under 2%. If you compare that against historic controls, it’s real favorable, particularly in the rectal domain,” he said. “I expected low risk to do well (97.3%) but didn’t figure intermediate risk to show 97%; that’s better than I thought.”

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In his presentation at the ASTRO annual meeting, Dr. Meier showed how single-institution studies on the use of SBRT as the primary treatment for prostate cancer have illuminated the treatment as a cost-effective and faster alternative to IMRT.

Dr. Meier explained that although the study wasn’t powered to compare against other therapies, if you did make a comparison against other radiation therapies, it would score favorably.

“The response has been one of cautious enthusiasm,” Dr. Meier said. “The community of radiation oncologists is often reluctant to embrace advancements, so it may take a randomized trial for people to adopt this as a standard of care.”

There is one such study currently underway at the Royal Marsden Hospital in the United Kingdom, led by its medical director, Nicholas van As, MBBCH. The study by Dr. Meier and his team is also ongoing.

“We would like to have more than 5 years’ follow-up; we would like to see 8 years with some 10-year follow-up,” he said. “Our trial confirms that SBRT may be preferable to other treatment approaches for newly diagnosed cases of prostate cancer, including more aggressive disease.”

Dr. Meier discloses receipt of a research grant from Accuray.